Regex to get sorted vowels

Question

Hi I am working on a piece of code, which opens a file that contains some random words like this:

semiconventional
superdeclamatory
semimathematical
semigeometric
stoloniferously
subacademical
supermathematical

Code as follows:

$handle = fopen($filename, "r");
$contents = fread($handle,filesize($filename));
$contentsArray = explode("\n",$contents);
$length = count($contentsArray);

echo "<pre>";

foreach ($contentsArray as $word) {
    if(preg_match("/(?=([aeiou]){3}([^aeiou])$)/", $word, $matches)){
        print_r($word);
        echo "\n";
    }
}

This code is printing all words which,

• Have at least 3 vowels (a,e,i,o,u)
• Does not end with a vowels (a,e,i,o,u)

My requirement is to get only those words which

• Does not end with a vowel (a,e,i,o,u)
• Have at least 3 vowels (i.e. a, e, i, o, u) which do not have to be unique, but must be in lexicographic order (i.e. the second vowel is equal to or comes after the first in the alphabet. For example, diamond would not qualify even though it has at least 3 vowels because the third letter “a” is lexicographically before the second letter “i” in the alphabet. However, catharsis would qualify because the vowels are “a”, “a”, “i”, and they are in lexicographic order in the sequence in which they appear in the word.

Answer 1

Here's a regex, just because:

^(?=(?:.*?[aeiou]){3})(?!.*u.*[aeio])(?!.*o.*[aei])(?!.*i.*[ae])(?!.*e.*a).*[^aeiou]$

regex101 demo.

---

Explanation:

^ # start of string anchor
(?= # make sure there are (at least) 3 vowels:
    (?:
        .*? # match any text,...
        [aeiou] #... and a vowel
    ){3} # 3 times
)
(?! # make sure there is NO occurence of
    .*u # a "u" character
    .*[aeio] # followed by an "a", "e", "i" or "o" character
)
(?!.*o.*[aei]) # similarly, make sure there's no "a", "e" or "i" after an "o"
(?!.*i.*[ae]) #... no "a" or "e" after an "i"...
(?!.*e.*a) #... and no "a" after an "e"
.*[^aeiou]$ # finally, make sure the last character is not a vowel.

Answer 2

The following forces monotonous vowel progression, but doesn't require any vowels at all, and will match anything ending in a consonant within those constraints.

^([^aeiou]*a)*([^aeiou]*e)*([^aeiou]*i)*([^aeiou]*o)*([^aeiou]*u)*[^aeiou]+$

You could augment it with a lookahead assertion at the beginning to force 3 or more vowels. Here is a regex which does that: it specifies three repetitions of vowels, interspersed by optional non-vowels:

([^aeiou]*[aeiou]){3}

Combining the two, we obtain

^(?=([^aeiou]*[aeiou]){3})([^aeiou]*a)*([^aeiou]*e)*([^aeiou]*i)*([^aeiou]*o)*([^aeiou]*u)*[^aeiou]+$